Radio receiving apparatus



Panis@ B. B. MINNIUM RADIO RECEIVING APPARATUS Filed June 23,

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Patented Jan. 21, 1930 UNITED STATES PATENT OFFICE BYRON B. MINNIUM, OF CHICAGO, ILLINOIS, ASSIGNOR TO WALTER H. HUTH, OF

CHICAGO,

ILLINOIS RADIO RECEIVING APPARATUS Application filed .Tune 23, 1925. Serial No. 39,031.

This invention relates to radio receiving set amplifiers of the kind 1n Which the capacity 1s so arranged, in relation to the grid to plate capacity, that a Vheatstone 3 bridge effect is produced, With capacity in each arm thereof, thereby to prevent the so-called back feed or inclination on the part of the apparatus to reverse itself, so to speak, and throw off or radiate energy Waves from 10 the aerial or other energy gathering means through which the receivingr set receives the messages. j

Generally stated, the object of the invention is to provide an improved method of progres- 113 sively introducing' a desired amount of what may be called an unbalanced condition into an amplifier circuit, by adjustment of the capacity thereof, thereby to insure'a uniform amplification over the entire timing range of 2U the amplifier circuit, by permitting just enough regeneration to accomplish the desired result, but in a Way which Will prevent at all times any undesirable oscillation or feed back. y

It is also an object to provide certain details and features of construction and combinations tending to increase the General efiiciency and the desirability of a l' heatstone bridge amplifying circuit of this particular character. y

To the foregoing and other useful ends,

the invention consists in the matters hereinafter set forth and claimed, and shown in the accompanying drawings, in Which,-

5 Fig. l is a diagram of a radio receiving apparatus embodying the principles of the invention. j

Fi 2 is a simplified diagram of the Wheatstone bridge arrangement or effect involved in the circuit arrangement shown in Fig. l

of the drawings, in the rst step of amplitication thereof.

As thus illustrated, the invention comprises an aerial l, or any suitable energv collecting means, connected to ground 2 through the primary 3 of an ordinary transformer or induction coil. The secondary 4 of said coil has one terminal thereof connected to the grid 5 of an ordinary vacuum tube or lamp, and has the other terminal thereof connected through the adjustable condenser G to the plate T of said vacuum tube. The two variable condensers 8 and 9 are connected in series between the terminals of the secondary coil, in the manner shown, forming a sort of bridge between the tvvo parallel circuit conductors lO and l1, and the intermedial point l2 of this condenser bridge is connected to one terminal of the filament 13 of said vacuum tube, While the other terminal of said lila-ment is connected to one pole of the battery la, as shown. The other pole of this battery is connected through the variable resistance l5 to the terminal of the lilament which is connected to the intermedial point 12, and between the conductors ll and 16 there is a variable condenser 17 of any suitable character. At 18 is `indicated in dotted lines the capacity which is ordinarily found to exist between the grid and the plate of the vacuum tube, while at 19 is indicated in dotted lines the capacity which ordinarily exists between the grid and the filament, although this capacity is very slight and is j n'actically negligible. The plate 7 is connected through the primary Q0 to one pole of the battery 2l, as shown, the other pole of this battery being connected through a conductor 22 to the conductor 23, which connects one pole of the battery 14 to one terminal of the iilament. Thus the output of the said vacuum tube or lamp is transmitted to the secondary 24E, from the primary 20, and from this on the receiving apparatus can be of any suitable or desired character, the arrangement shown being a common one and one that will be readily understood.

Now7 in Fig. 2 is shown the heatstone bridge arrangement involved in the receiving circuits. The arm 25 contains the capacity formed by the condenser 8, while the arm 26 contains the capacity provided by the condenser l), While the arm 27 contains the capacity developed between the grid 5 and the plate 7, and the arm 28 contains the capacity 6 previously mentioned. The input conductors, and the output conductors, are connectedkas shown, so that the four arms of the VVheatstone bridge are interposed in the manner shown between the input circuit and nl u the output circuit of the amplifying circuit. 'l his v\'\"heatstene bridge arrangcnient, thus formed, in practice tends to prevent the troublesome feed back, or regeneration and inclination of the apparatus to reverse itself, so to speak, and to throw off energy from the receiving aerial, and prevents oscillation.

However, some regeneration is found to be desirable, in order to insure amplification over the entire tuning range of the amplifier, and for this purpose some degree or extent of unbalanced condition of the capacity, as between the condensers 8 and 9, is found to be desirable. This may be accomplished, for example, by making the condenser 9 somewhat larger than the condenser 8, so that the condenser 9 will have the greater capacity of the two, and by placing both of these condensers on the same shaft (not shown), so that both condensers will be adjusted simultaneously in the tuning of the apparatus. lith this, and with the capacity 19 such that the ratio between arm 25 and arm 26 is the same as the ratio between arm Q7 and arm 28, when condensers 8 and 9 are adjusted for their minimum capacity, the lVheatstone bridge is balanced against regeneration, if condenser (i is properly adjusted. New, by increasing the capacity of condensers 8 and 9. while capacity 19 remains fixed, the ratio between arms 25 and Q6 does not remain constant. This will bring about some regeneration, and for the regulation thereof the adjustable condenser 17 is provided, so that any degree of unbalance can be brought about for any particular wave length, as with some wave lengths practically no unbalanced condition will be necessary, while other wave lengths would require some unbalanced condition, in order to increase the sensitiveness and insure proper tuning of the apparatus. Therefore, by adjusting the condenser 17, the exact condition of balance or unbalance can be obtained, necessary to the proper tuning of the apparatus, but at the same time the lVheatstone bridge will function to prevent any undesirable feed back or inclination on the part of the apparatus to throw oit energy through the aerial, this feed back being something which is well known and understood. Such feed back is sometimes very troublesome, not only because it somewhat interferes with the proper functioning of the receiving set, but also because it may become annoying to others having receiving near b v. The relation of the condenser 17 to the YVheatstone bridge is shown in Fig. Q, and it will be seen that with this arrangement the two condensers 8 and 9 can be adjusted simultaneously, and if the arm 26 is then found not to have the correct amount of capacity therein, the condenser 17 can then be adjusted to bring about the desired efi'ect.

In this way, therefore, the ratio between the capacities 8 and 9 remains fixed, and

while this ratio might not be proper for certain adjustments, or might not be the best that could be had for some wave lengths, yet it can be corrected or made satisfactory, so to speak, by adjustment of the condenser 17, in the manner explained. Thus the lVlieatstone bridge arrangement will function at all times to prevent any undesirable amount of feed back, but at the same time sufficient regeneration will be permitted, when needed, to insure the sensitiveness and proper tuning effect necessary or desirable for any particular wave length, for in some cases a little regeneration does improve the sensitiveness and tends to insure a more uniform amplification over the entire tuning range of the an'iplifier.

Thus the two condensers S and 9, mounted on the same shaft, for example, will maintain a fixed ratio between them, but the capacity of one condenser is always greater than the other, so that the ratio between arms 25 and 26 will always be the same, notwithstanding the greater capacity of one, except for the provision of the condenser 17 connected in multiple with the condenser 9 in the manner shown and described, and except for the condenser 19 which remains fixed. Capacity 19 is connected in multiple with the condenser S, as shown by the simplified diagram in Fig. 2 of the drawings.

It will be seen, therefore, that the secondary t is, in the diagram shown in Fig. 2, connected in the indicated input circuit, and is thus connected between opposite junctions of the lVheatstone bridge, or between the upper and lower corners of the diagranunatic Theatstone bridge shown in Fig. 2 of the drawings. And, of course, it will be understood that the expression vacuum tube is used in a generic sense and intended to include all devices of the type adapted to amplify radio frequency current-s by a voltage control of a space current.

In use, it is only necessary for the user of the receiving set to adjust the condensers 8 and 9 of the lVheatstone bridge arrangement, as the condensers G and 17 may be adjusted and set in position or such adjustment as will answer the purpose for all adjustments of the two simultaneously adjustable condensers. The point of balance, or approximate balance, may be at either end of the range of adjustment of the two condensers 8 and 9, or such point may be at the middle of said range of adjustment. In any event, throughout some portion of the range of adjustment the unbalancing of the Theatstone bridge is progressive, obviously, and when such motion is reversed the gradual return to a more balanced condition is also pro gressive. Thus the unbalancing is automatic, so to speak, as it is accomplished simply by the simultaneous adjustment of the condensers 8 and 9, and the progressive unbalancing is incidental to this adjustment. The manufacturer inay adjust the condensers 6 and 17, and set them in properly adjusted position, and the tuning of the apparatus for different wave lengths, with more or less unbalance of the Wheatstone bridge arrangement, is then brought about by simply adjusting the two condensers 8 and 9, these two condensers vbeing coupled together for simultaneous adjustment only, whereby the more or less unbalancing of the Wheatstone bridge arrangement is incidental and unavoidable in the tuning of the receiving set for different wave lengths, and is predetermined by the relative formation and construction of the dierent condensers.

Without any intent to disclaim any novelty over the prior art, shown in the drawing or described in the specification, what I claim as my invention is:

l. In a radio receiving set amplifier, means forming in effect a VVheatstone bridge arrangement, with capacity in each arm thereofi, and with the ordinary grid to plate cay pacity of the amplifier forming the capacity in one arm, two other arms each having the capacity thereof adjustable for tuning the receiver for different wave lengths, and other adjustable capacity connected in multiple with said adjustable capacity of one of said arms and in effect operative when in set position to automatically vary the ratio between said adjustable capacity arms by the adjustment of said tuning capacity.

2. A structure and circuit arrangement as specified in claim l, said first mentioned adjustable capacity arms being adjustable in unison only, whereby said other adjustable capacity is operative to change the ratio between said two other arms.

A structure and circuit arrangement as specified in claim l, one said first mentioned adjustable capacity being greater in one arm than the capacity in the other arm, and said last mentioned adjustable capacity being in multiple with the said greater capacity.

4L. A structure and circuit arrangement as specified in claim l, comprising a repeating coil having the secondary thereof connected between opposite junctions of said bridge, one said junction being between arms each containing adjustable capacity, and the other junction being between arms one containing adjustable capacity and the other containing said grid-to-plate capacity.

5. A structure and circuit arrangement as specified in claim l, said two adjustable capacity arms being adjustable in unison only, and the adjustable capacity of one arm being greater than the adjustable capacity of the other arm, and said other adjustable capacity and said greater arm capacity being connected in multiple.

6. A structure and circuit arrangement as specified in claim 1, the two adjustable capacity arms comprising two separate condensers, one of greater capacity than the other, mounted on the same shaft, and thereby necessarily adjustable in unison, and the said other adjustable capacity being connected in multiple with said greater capacity.

7. In radio apparatus, the combination ot instrumentalities forming in effect a Theatstone bridge arrangement having condensers `in two of the arms thereof, the two condensers being connected together for siinultaneous adjustment only, a capacity in shunt of one of said condensers, and a capacity in another arm ott said VVheatstone bridge arrangement, said condensers being relatively formed to co-operate with each said capacity to progressively imbalance the bridge by the simultaneous adjustment of said condensers in one direction, and to progressively restore the bridge to a more balanced condition by adjustment in the opposite direction.

8. A structure as specified in claim 7, in combination with other elements forming with said Theatstone bridge arrangement a radio circuit which can be tuned for different wave lengths by the said simultaneous adjustment of said condensers, whereby there will be a greater unbalance of the bridge for some wave lengths than for others.

9. A structure as specified in claim 7, in combination with elements forming with said lVheatstone bridge arrangement a radio receiving apparatus which can be tuned for different wave lengths by the said simultaneous adjustment of said condensers, and each said capacity being an adjustable condenser which can be set at a desired fixed adjustment for all adjustments ot said siinultaneously adjustable condensers.

l0. A structure as specified in claim 7, each said capacity being an adjustable condenser which can be set at a desired fixed adjustment for all adjustments of said simultaneously adjustable condensers.

Specification signed this 12th day of June,

BYRON B. MINNIUM. 

